Apparatus and method for coating pipes

ABSTRACT

Apparatus for coating pipes includes means for applying a sheet material  32,33,34 , to a pipe  2  and means for heating  23,31  the sheet material and/or pipe. The means for heating may be operative to heat the sheet material during its application to the pipe. The means for heating may comprise a means for directing hot air towards the pipe and/or sheet material. The sheet material may be disposed on reels housed in canisters  22  that are releasably mounted on the apparatus.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and method for coatingpipes and particularly, but not exclusively, girth welds on oil and gaspipelines.

Oil and gas pipelines are usually formed from many lengths of externallycoated steel pipe welded together. The pipes are coated to preventcorrosion. They are usually coated at a factory remote from the sitewhere they are to be laid. This is generally more cost effective thancoating them on site. At the factory a coating is applied to the outsideof the pipes leaving a short length uncoated at each end. This isnecessary to enable the pipes to be welded together end-to-end on siteto form a pipeline. Each resulting girth weld and adjacent uncoatedregion of the pipe must be coated before the pipeline is laid. Thiscoating is known as the field joint coating. Ideally, the properties ofthe field joint coating should match those of the factory appliedcoating applied to the remainder of the pipes.

In one known arrangement the factory applied coating comprisespolypropylene and the field joint coating is formed by polypropylenetape wound helically over the field joint area and factory appliedcoating adjacent the field joint area. Each turn of the tape overlapseither part of the factory applied coating or a previous layer or layersof tape by a predetermined amount.

A known method of applying a polypropylene tape field joint includes thefollowing steps. The surface of the factory applied coating which willbe overlapped by tape is cleaned and masked. The field joint area isthen abrasive blast cleaned and induction heated. A layer of fusionbonded epoxy powder is applied to the field joint area, followed by alayer of polypropylene powder. The heat in the pipe causes the epoxypowder to bond to the pipe, the polypropylene subsequently bonds withthe epoxy as it melts and flows to cover the surface of the field joint.The masking on the adjacent factory applied coating is now removed. Thesurface of the factory applied coating will now have been heated byconduction of heat through the coating from the pipe, but not so much asit melts. A layer of molten polypropylene is then applied to the surfaceof the factory coating to be overlapped by tape using a flame sprayingprocess.

Polypropylene tape is now wrapped helically across the field joint areaand adjacent factory applied coating. Residual heat in the pipe andfactory applied coating from induction heating and subsequent flamespraying causes the surface of the polypropylene tape brought intocontact with the pipe or factory applied coating to melt so that thetape becomes welded to the pipe or coating on cooling. Bonding ofoverlapping layers of tape together occurs through conduction ofresidual heat in the pipe through an underlying layer of tape to anoverlying layer of tape sufficient to cause the abutting surfaces of thetape layers to melt. Bonding of layers of tape may also be facilitatedby the subsequent external application of heat to the tape using a gasflame.

A problem with this existing method is that heating of the factoryapplied coating and molten polypropylene bonded thereto during the flamespraying is difficult to control. The margin between insufficientheating, leading to poor bonding between factory applied coating andtape, and overheating, causing burning of the factory applied coating orapplied molten polypropylene which also adversely affects bonding withtape, is very narrow. In practice it is difficult to achieveconsistently good bonding.

Another problem arises because the polypropylene applied to the factorycoating remains molten for a limited period only. If there is too greata delay before application of tape the polypropylene can begin tosolidify making it unlikely that tape will bond properly to it. This canhappen, for example, where two turns of tape are required to coat thefactory applied coating and the polypropylene solidifies betweenapplication of the two turns, and where the factory coating adjacent oneside of a field joint is coated with tape before that at the oppositeside of the joint.

Another problem is poor bonding between layers of tape. Bonding occursthrough conduction of residual heat from the pipe and/or application ofheat externally using a gas flame. Application of external heat is, inpractice, largely ineffective in heating up a thickness of tape and itcan take a considerable amount of time for sufficient heat to causebonding to be conducted through layers of tape from the pipe itself. Asthe field joint coating increases in thickness there becomes a pointwhere sufficient heat to cause satisfactory bonding cannot be conductedfrom the pipe. Further, because it is often necessary to force quench afield joint to solidify the polypropylene coating in order for it towithstand mechanical loading, for example from pipe rollers, and in manyinstances offshore a finished field joint is immersed in the sea withintwo or three minutes of application, regardless of its thickness a jointis often cooled before bonding between tape layers is complete. Also,the application of external heat using a gas flame despite being largelyineffective is also imprecise and can easily result in burning orcomplete melting of the outside of the coating, both of which areundesirable. As interlayer bonding and adhesion to the factory coatingcannot be verified other than by destructive testing there can be littleconfidence in the integrity of a finished field joint coating.

SUMMARY OF THE INVENTION

The present invention seeks to overcome, or at least mitigate, theabovementioned problems.

According to a first aspect of the present invention there is providedapparatus for coating pipes comprising means for applying a sheetmaterial to a pipe, means for heating the sheet material and/or pipe anda releasably mounted canister housing a reel for supplying sheetmaterial in the form of a tape which may be withdrawn from the canister.

The means for heating the sheet material and/or pipe is preferablyoperative to heat the sheet material and/or pipe during application ofthe sheet material to the pipe. Provision of means for heating enablesthe surface of a pipe, either coated or uncoated, and/or sheet materialbeing applied to the pipe to be brought to a sufficient temperature toensure good bonding of the sheet material and pipe on first applicationobviating the need for post application heating and increasing theintegrity of an applied coating.

Housing reels in canisters helps to preserve the temperature ofpreheated reels. The canisters may include means for heating, operativeto heat a reel disposed therein.

According to a second aspect of the present invention there is provideda method for coating a pipe by application of a sheet material includingthe steps of preheating the sheet material using a first heating meansprior to application of the sheet material to the pipe, and heating thepipe and/or sheet material using a second heating means during theapplication of the sheet material to the pipe.

The pipe and/or sheet material is preferably heated with hot air and theapparatus preferably includes means for directing hot air towards thepipe and/or sheet material. The use of hot air, of which it is possibleto control the temperature, reduces the risk of burning a coatingcompared with the use of a gas flame.

The sheet material may be preheated in an oven. The sheet material ispreferably a tape.

The apparatus is preferably arranged to apply tape to a pipe in ahelical pattern. The apparatus preferably includes means for tensioningtape as it is applied to the pipe and means for urging tape onto thepipe. Both means may comprise rollers. The apparatus preferably includesa stator and a rotor, rotatably mounted on the stator for rotationaround the periphery of a pipe. The apparatus also preferably comprisesmeans to move at least part of the rotor longitudinally along the pipe.The means to move at least part of the rotor longitudinally along thepipe may be driven by the rotor, more particularly by relative movementof the rotor and stator. This drive can preferably be disengaged toallow movement of the means to move at least part of the rotorlongitudinally along the pipe independently of relative rotation of thestator and rotor. One or more tape reels may preferably be releasablymounted on the rotor. The means for heating, for example hot airblowers, is preferably also mounted on the rotor. The stator and rotorpreferably comprise an electrical contact arrangement to supplyelectrical power to the means for heating which permits continuousrelative rotation of the rotor and stator through an unlimited number ofturns. The electrical contact arrangement may comprise one or moreelectrical slip rings mounted on either the stator or rotor and one ormore associated electrical brushes mounted on the other of the stator orrotor.

Both the stator and rotor preferably comprise rings formed from two ormore pivotally connected components so that they may be opened formounting and demounting on a pipeline.

In another arrangement the stator and/or rotor is of a horseshoe shape.In another arrangement the apparatus comprises a body arranged to bemovably mounted on a pipe, in particular to be mounted for rotationabout a pipe.

The apparatus and method according to the invention enable rapid andreliable application of a field joint coating using tape such aspolypropylene tape. Provision for heating during application of tapeenables the surface to which the tape is applied and/or the tape itselfto be heated sufficiently to form an effective bond. The need for postapplication heating or a lengthy delay to allow the coating to be heatsoaked from residual heat in the pipe is overcome. The time required toapply a coating is therefore also reduced and while this is alwaysadvantageous it is particularly so where offshore pipelines areconcerned as quenching of the coating by immersion in the sea will notadversely affect the integrity of the coating.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

In order that the invention may be more clearly understood an embodimentthereof will now be described by way of example with reference to theaccompanying drawings of which:

FIG. 1 is an end view of apparatus according to the invention mounted ona pipeline;

FIG. 2 is an enlarged end view of part of the apparatus of FIG. 1mounted on a pipeline;

FIG. 3 is an enlarged view of a reel canister of the apparatus of FIG. 1with some internal detail shown with broken lines; and

FIG. 4 is a side view of the apparatus of FIG. 1 mounted on an uprightpipeline.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings show apparatus for applying a tape, particularly apolypropylene tape, to the field joint of a pipeline. The illustratedapparatus is primarily intended for use on an upright pipe such as theend of an offshore pipeline being laid using the J-lay technique. Inthis arrangement short lengths of pipe are welded together to form apipeline and the field joints coated immediately prior to immersion ofthe pipeline into the sea. Rapid application of high integrity fieldjoint coatings is therefore necessary.

Referring to the drawings the apparatus comprises a fixed ring 1 formedfrom two pivotally connected parts which may be opened to allow the ring1 to be placed around and removed from a pipeline 2. When placed arounda pipeline 2 the two parts of the ring are fastened by a releasablelatch 3. In use the fixed ring 1 is mounted on a track guided wheeledcarriage (not shown) which enables the fixed ring 1 to be moved radiallyrelative to a pipe to be coated.

A rotating ring 4, also formed from two pivotally connected componentsconnectable by a releasable latch 5, is mounted on the fixed ring 1 forrotation relative thereto. The rotating ring 4 is supported on ballrollers 6 disposed on the surface of the fixed ring 1. The rotating ring4 is also constrained radially relative to the fixed ring 1 by guidewheels 7 mounted on the fixed ring 1 and arranged to run against theinside of the rotating ring 4.

A drive motor 8 mounted on the fixed ring 1 drives a drive wheel 9 whichis in driving contact with the periphery of the rotating ring 4. Thisenables the rotating ring 4 to be rotated relative to the fixed ring 1.

The surface of the rotating ring 4 facing the fixed ring 1 includes anumber of electrical contact slip rings 10, the path of which isindicated by broken lines 11 in FIG. 1. The facing surface of the fixedring includes a number of electrical contact brushes 12 which are urgedinto sliding contact with the slip rings 11. The purpose of the slipring and brush arrangement is described below.

Extending axially from the rotating ring is a support tower 13 housing alead screw 14 mounted between bearings 15. The lead screw 14 is drivenby a drive belt 17. The belt 17 is driven by a drive wheel 18 which is,in turn, driven by a cylindrical portion 19 of the fixed ring 1. Theapparatus is arranged so that as the rotating ring 4 is driven relativeto the fixed ring 1 this causes the lead screw 14 to rotate. The drivewheel 18 may be moved radially of the cylindrical portion 19 of thefixed ring 1 so as to move the wheel into and out of driving engagementwith the cylindrical portion 19. This allows the lead screw 14 to berotated independently of rotation of the rotating ring 4 relative to thefixed ring.

The lead screw 14 and support tower 13 support a drive block 20,threadedly engaged with the lead screw 14 so that it advances along thelead screw 14 in response to rotation thereof.

A support arm 21 is mounted on the drive block 20 and extends in an arcfrom opposite sides thereof. Disposed on the support arm 21 are twomountings for supporting canisters, two pairs of hot air blowers 23 andtwo pressure roller assemblies 24.

Each canister 22 houses a reel 25 of polypropylene tape 26, and includesa tension roller assembly. This comprises a silicone rubber roller 27rigidly mounted on a shaft 28 supported between two pivotally connectedarms 29 resiliently urged together by springs 30. The arms 29 act as abrake on the roller 27, increasing the force required to pull tape 26out of the canister 22 over the roller 27 thereby ensuring that adesired tension can be maintained in the tape 26 as it is withdrawn fromthe canister.

Each hot air blower 23 includes a nozzle 31 for directing hot airtowards the surface of a pipeline 2 on which the apparatus is mounted ortowards both the surface of the pipeline 2 and of tape 26 withdrawn fromone of the canisters 22. The hot air blowers are electrically operated.Electrical current is supplied to the blowers via the brushes 12 andslip rings 10. The blowers 23 supply air at a temperature of about 600°C.

Each pressure roller assembly 24 comprises a silicone rubber roller 32rotatably mounted on a pivotally supported arm 33 resiliently urgedradially inwardly of the support arm 21 by a spring 34 so that, in use,the surface of the roller 32 is urged against the surface of a pipeline2 on which the apparatus is mounted.

A coating is applied to the field joint region 35 of a pipeline 2 usingthe apparatus as follows. First, the field joint region 35 and factorycoating adjacent the field joint region 35 is prepared by cleaning,induction heating of the pipeline and application of epoxy andpolypropylene powders to the heated field joint region 35. Next, acanister 22 or canisters of tape 26 which has/have been heated to apredetermined temperature is/are mounted on the support arm 21 of theapparatus. The fixed and rotating rings 1,4 are now placed around thepipeline, closed and latched. The apparatus is positioned so that thetape canister(s) 22 partially overlap the factory applied coatingadjacent the field joint area with the drive block 16 disposed at oneend of its travel along lead screw 14.

A length of tape 26 is withdrawn from each canister 22 over the tensionroller 27, and brought into contact with the surface of the pipeline 2,passing under the pressure roller 32.

The hot air blowers 23 are now started (alternatively they could havealready been running), followed by the drive motor 8. This causes therotating ring 4 to rotate around the pipeline 2 and the drive block 20to advance along the drive screw 14 so that the tape is applied to thesurface of the pipeline in a helical pattern with a degree of overlap,typically each fresh layer of tape overlaps the previous layer by abouttwo thirds of its width. The hot air blowers 23 heat the surface of thepipeline 2 and, to some extent, the tape 26 immediately prior toapplication of the tape 26 to the pipeline 2. This ensures that thesurface of both the tape 26 and pipeline (coated or not) aresufficiently hot to form an effective bond.

The tape 27 is dispensed at a predetermined tension which is controlledby the tension roller in the canister. Immediately after the tapecontacts the pipe surface it is pressed against that surface by apressure roller 32.

The first portion of tape is applied to a surface which has not beenpreheated and therefore does not bond to the surface. The tape issubsequently peeled from the surface until the point at which bondingstarts is found. The tape is cut at this point and removed.

When the field joint area 35 has been wrapped with tape 26 this is cutand the apparatus removed from the pipe. The coating is now complete, nofurther heating is necessary as each tape/pipe, tape/coating andtape/tape interface has been heated prior to being brought together,there is no need to wait for heat to pass through the coating frominside (from the pipe) or externally. This saves time and leads to animproved coating.

The speed of operation of the apparatus may be varied by varying thespeed of the drive motor 8. Slowing the machine allows for more heatingof the pipe/tape prior to application of tape. Typically the apparatuswill be run slowly when applying tape over the factory coating, but morequickly when applying tape over the heated pipe for the first time. Theapparatus would be run more slowly for application of a second orsubsequent layer of tape, because of the need to heat the previous layerof tape sufficiently to effect a satisfactory bond.

Following application of tape to a field joint the drive motor 8 and hotair blowers are stopped, the fixed 1 and rotating 4 rings opened and theapparatus moved radially away from the pipeline. Drive wheel 18 is thendisengaged from the cylindrical portion 19 of the fixed ring 1 and thelead screw 14 rotated to return the drive block 20 and hence support arm21 back to its original position ready to coat another field joint.

In an alternative embodiment the apparatus could be adapted to be run inreverse so that tape can be applied to a field joint irrespective of thedirection of travel of the support arm relative to the fixed androtating rings 1,4. This might be achieved, for example, by providingtape canisters and pressure roller assemblies for dispensing tape inboth directions of relative rotation of the fixed and rotating rings1,4.

The above embodiment is described by way of example only. Manyvariations are possible without departing from the invention.

1. Apparatus for coating pipes comprising: means for applying a sheetmaterial to a pipe; first means for pre-heating the sheet material priorto applying the sheet material to the pipe; a canister housing a reelfor supplying sheet material in the form of a tape which may bewithdrawn from the canister, said canister being configured and arrangedto releasably couple to said apparatus itself; and second means forheating the pipe as the sheet material is being applied to the pipe. 2.Apparatus as claimed in claim 1, wherein the second means for heating isoperative to heat the sheet material and pipe during application of thesheet material to the pipe.
 3. Apparatus as claimed in claim 1, whereinthe first means and the second means for heating includes means fordirecting hot air towards the pipe and sheet material.
 4. Apparatus asclaimed in claim 1 for applying sheet material in the form of a tape toa pipe in a helical pattern further including means for tensioning thetape as it is applied to the pipe, said means for tensioning the tapeincluded in said canister; and means for urging the tape onto the pipe.5. Apparatus as claimed in claim 1 for applying sheet material in theform of a tape to a pipe in a helical pattern further including meansfor tensioning the tape as it is applied to the pipe, said means fortensioning the tape included in said canister, means for urging the tapeonto the pipe, a stator for mounting on a pipe and a rotor, rotatablymounted on the stator for rotation around the periphery of the pipe. 6.Apparatus as claimed in claim 1 for applying sheet material in the formof a tape to a pipe in a helical pattern further including means fortensioning the tape as it is applied to the pipe, said means fortensioning the tape included in said canister, means for urging the tapeonto the pipe, a stator for mounting on a pipe, a rotor rotatablymounted on the stator for rotation around the periphery of the pipe, anddrive means to move at least part of the rotor longitudinally along thepipe.
 7. Apparatus as claimed in claim 1 for applying sheet material inthe form of a tape to a pipe in a helical pattern further includingmeans for tensioning the tape as it is applied to the pipe, said meansfor tensioning the tape included in said canister, means for urging thetape onto the pipe, a stator for mounting on a pipe, a rotor rotatablymounted on the stator for rotation around the periphery of the pipe, anddrive means to move at least part of the rotor longitudinally along thepipe, wherein the drive means is driven by relative movement of therotor and stator.
 8. Apparatus as claimed in claim 1 for applying sheetmaterial in the form of a tape to a pipe in a helical pattern furtherincluding means for tensioning the tape as it is applied to the pipe,said means for tensioning the tape included in said canister, means forurging the tape onto the pipe, a stator for mounting on a pipe, a rotorrotatably mounted on the stator for rotation around the periphery of thepipe, and drive means to move at least part of the rotor longitudinallyalong the pipe, wherein the drive means is driven by relative movementof the rotor and stator, and the drive means can be disengaged to allowmovement of the at least part of the rotor longitudinally along the pipeindependently of relative rotation of the stator and rotor.
 9. Apparatusas claimed in claim 1 for applying sheet material in the form of a tapeto a pipe in a helical pattern further including means for tensioningthe tape as it is applied to the pipe, said means for tensioning thetape included in said canister, means for urging the tape onto the pipe,a stator for mounting on a pipe and a rotor, rotatably mounted on thestator for rotation around the periphery of the pipe, wherein the meansfor heating is mounted on the rotor.
 10. Apparatus as claimed in claim 1for applying sheet material in the form of a tape to a pipe in a helicalpattern further including means for tensioning the tape as it is appliedto the pipe, said means for tensioning the tape included in saidcanister, means for urging the tape onto the pipe, a stator for mountingon a pipe and a rotor rotatably mounted on the stator for rotationaround the periphery of the pipe, wherein the rotor comprises means forreleasably supporting a reel of tape.
 11. Apparatus as claimed in claim1 for applying sheet material in the form of a tape to a pipe in ahelical pattern further including means for tensioning the tape as it isapplied to the pipe, said means for tensioning the tape included in saidcanister, means for urging the tape onto the pipe, a stator for mountingon a pipe and a rotor, rotatably mounted on the stator for rotationaround the periphery of the pipe, wherein the stator and/or rotorcomprise rings formed from two or more pivotally connected components.12. Apparatus as claimed in claim 1, wherein the canister includes thesecond means for heating and is operative to heat a reel of tapedisposed therein.